(a) Field of the Invention
The present invention relates to a method for manufacturing a resonator which is applicable to filters for electronic circuits. In particular, it relates to a method for manufacturing a film bulk acoustic resonator.
(b) Description of Related Art
Film bulk acoustic resonators (hereinafter referred to as FBARs) have been used for high frequency filters of high performance. In recent years, with a decrease in size and an increase in frequency band of high frequency devices such as cellular phones, expectations have been placed on the application of the FBARs.
In the manufacture of the FBARs, the most important step is to form a structure for resonating acoustic waves. Such a structure has been formed by known methods, for example, by forming a trench from the bottom surface of a substrate to a lower electrode by etching, forming an air gap (air bridge) or forming a multilayer acoustic film.
Hereinafter, with reference to FIGS. 8 and 9, an explanation is given for examples of the conventional methods for forming the FBARs.